26 Sep
2008
26 Sep
'08
6:12 p.m.
On Fri, Sep 26, 2008 at 5:37 PM, Andrew Coppin
As already noted, Data.Set *should* be a Monad, but can't be. The type system won't allow it. (And I know I'm not the first person to notice this...)
I wouldn't say that. It's important to remember that Haskell class
Monad does not, and can not, represent *all* monads, only (strong)
monads built on a functor from the category of Haskell types and
functions to itself.
Data.Set is a functor from the category of Haskell types *with
decidable ordering* and *order-preserving* functions to itself. That's
not the same category, although it is closely related.
--
Dave Menendez